Been musing over this for a longassed time. Decided on a streetport 13B. Of sorts.
GSL-SE front and rear irons and rotor housings because of where the o-rings are, S5 rotating assembly because of weight issues, and 12A center iron because... well, have you ever seen the 13B primary ports? They suck. The 12A ones are about the size of the TurboII secondary ports. All of these irons and housings with an EProd spec port job (beyond actually; filling in areas with devcon too for smoothness) and some oiling mods. Header too of course... know someone who made a jig off of their race 13B header.
Induction through a modified S4 NA intake manifold. Places for the 5th and 6th port actuators filled in with devcon and ported smooth, a lot of extraneous emissions stuff ground off, and the crosstubes cut off. Did some measuring and machining, and it's doable to ditch the UIM part of that and attach bike throttle bodies there. Nice thing is that with the bike injectors and a pair of T2 injectors plugged into the intake manifold, I should have enough fuel without milling the center iron for injectors like Mazda did. Megasquirted of course.
Driveline / Brakes / Suspension
The fun part is that I found out someone finally got Moser to make 5x4.5" rear axles for the 1st gen RX-7. Which means that I can have an intermediate step in brake upgrades by just using the T2 stuff I've got laying around. Also ditching the stock booster and master cylinder and going to a non-assist dual-MC setup; tried it before and like how it feels.
Suspension's easy; largely copy what we did on the race car. G-Force trilink because there's some aspects of it I can't easily fabricate myself, and my own panhard bar and turn-in spacers because those I can fabricate. Coilovers, springs and shocks... hell, we have those as spare parts! Maybe some lowering too, y'never know.
... best part is that most of the bits are laying around and, aside from possibly eventually upgrading away from stock (TurboII) brakes to Wilwoods, that's about everything I want to do to a street FB.